Field of the Invention
The present invention generally relates to the field of biotechnology. More specifically, the invention relates to recombinant DNA molecules encoding enzymes that degrade herbicides. The invention also relates to transgenic plants, parts, seeds, cells, and plant parts containing the recombinant DNA molecules, as well as methods of using the same.
Description of Related Art
Agricultural crop production often utilizes transgenic traits created using the methods of biotechnology. A heterologous gene, also known as a transgene, is introduced into a plant to produce a transgenic trait. Expression of the transgene in the plant confers a desirable trait, such as herbicide tolerance, on the plant. Examples of transgenic herbicide tolerance traits include glyphosate tolerance, glufosinate tolerance, and dicamba tolerance. With the increase of weed species resistant to the most commonly used herbicides, new herbicide tolerance traits are needed in the field. Herbicides of particular interest are the aryloxyphenoxypropionate (AOPP) herbicides, phenoxy acid herbicides, and pyridinyloxy acid herbicides. AOPP herbicides, phenoxy acid herbicides, and pyridinyloxy acid herbicides provide control of a spectrum of glyphosate-resistant weeds, thus making a trait conferring tolerance these herbicides particularly useful in a cropping system combined with other herbicide tolerance trait(s).
The Sphingobium herbicidovorans strain MH isolated from a dichloroprop-degrading soil sample was identified as being capable of cleaving the ether bond of various phyenoxyalkanoic acid herbicides, utilizing this as its sole carbon and energy source for growth (HPE Kohler, Journal of Industrial Microbiology & Biotechnology (1999) 23:336-340). Catabolism of the herbicides is carried out by two different enantioselective alpha-ketoglutarate-dependent dioxygenases, RdpA (R-dichloroprop dioxygenase) and SdpA (S-dichloroprop dioxygenase). (A Westendorf, et al., Microbiological Research (2002) 157:317-322; Westendorf, et al., Acta Biotechnologica (2003) 23(1):3-17). RdpA has been isolated from Sphingobium herbicidovorans (GenBank Accessions AF516752 (DNA) and AAM90965 (protein)) and Delftia acidovorans (GenBank Accessions NG_036924 (DNA) and YP_009083283 (protein)) (TA Mueller, et al., Applied and Environmental Microbiology (2004) 70 (10):6066-6075.) The RdpA and SdpA genes have been used for plant transformation to confer herbicide tolerance to crops (TR Wright, et al., Proceedings of the National Academy of Sciences USA, (2010) 107(47):20240-5). Improving the activity of the RdpA enzyme using protein engineering techniques to create a protein for use in transgenic plants would permit higher rates of herbicide application, thus improving transgenic crop safety and weed control measures.